Why Police Lineups Will Never Be Perfect

For three decades psychology researchers have been searching for ways to make eyewitness identifications more reliable. Many studies have shown, for example, the value of “double-blind” lineups, meaning that neither the cop administering the lineup nor the witness knows which of the photos, if any, is the suspect.

But injecting science into the justice system is tricky. For one thing, most criminal investigations happen at a local level. The U.S. has roughly 16,000 law enforcement agencies and few nationally mandated standards. The other big problem is the nature of science itself: Evidence for a given idea builds gradually, as scientists try to replicate others’ work. It can take years or even decades for a clear picture to emerge, and in the meantime scientists may vigorously disagree. While they argue, cases are opened and closed, and people, sometimes the wrong people, go to prison.

Some helpful guidance came today from the National Academy of Sciences. Last year the Academy asked a panel of top scientists to review technical reports and expert testimony about eyewitness identifications and make some solid recommendations. The resulting 160 page report offers many concrete suggestions for carrying out eyewitness identifications. For example, the Academy recommends using double-blind lineups and standardized witness instructions, and training law enforcement officials on the fallibility of eyewitness memory.

On one question, though, the Academy offers no clear answer: What’s the best way to present a photo lineup to a witness? This fuzziness reflects a hot debate bubbling in the scientific literature.